1. Field of the Invention:
This invention relates in general to earth boring machines and in particular to an improved kelly head for a hydraulic mast digger.
2. Description of the Prior Art:
Shallow holes for foundation piers and the like are often drilled with a hydraulically powered drilling machine known as a digger. The digger is usually truck mounted and has a hydraulic mast or cylinder twenty to thirty feet long. A square bar known as a kelly is rotatably carried in the hydraulic cylinder and rotatably driven by a hydraulic motor. The kelly has a kelly head at its top that serves as a piston for moving the kelly up and down in response to hydraulic fluid pressure in the hydraulic cylinder. The cutting tool secured to the bottom of the kelly is normally an auger containing helical flights.
The kelly head includes a set of bearings secured to the top of the kelly and mounted in a bearing sleeve. The bearing sleeve moves longitudinally in the hydraulic cylinder, and the bearings allow the kelly to rotate with respect to the bearing sleeve. A cap, also called a spindle, is secured to the top of the sleeve. The cap and bearing sleeve form a piston for movement in the cylinder in response to the hydraulic fluid pressure.
In one prior art model, the cap is secured to the bearing sleeve by screws that may loosen and cause damage. In another prior art model, the cap is secured by threads to the bearing sleeve. A pin is driven into a blind hole formed between the cap and bearing sleeve to prevent the cap from loosening. The disadvantage of this arrangement is that when access to the bearings is required, the pin must be drilled out. This is time consuming and may cause damage to the cap. In addition to providing an improved connection between the cap and bearing sleeve, increasing the life of the seals of the kelly head is also desirable.